Electric timepiece

ABSTRACT

An electric timepiece having a driving circuit having a single coil inserted between the collector electrodes of two transistors, one being of the NPN type, the other being the PNP type. A condenser is inserted between the collector electrode of one transistor and a base electrode of the other transistor, and a bias circuit for supplying self-bias is connected to the base electrode of the two transistors. The driving circuit may be utilized with a time standard oscillator including a tuning fork oscillator. Said tuning fork may be U-shaped, said single coil being mounted intermediate a U-shaped magnetic circuit mounted on a portion of said tuning fork.

United States Patent 1191 Tsuruishi 1111 3,744,233 [451 July 10,1973

1 ELECTRIC TIMEPIECE [75] Inventor: YukiTsuruishi, Suwa-shi,

Japan 221 Filed: Aug. 2, 1971 21 Appl. No.: 168,251

[30] Foreign Application Priority Data 58/23 V, 23 AC, 28 R, 28 A; 310/25; 318/126, 130;331/l54,l56

[56] 7 References Cited UNITED STATES PATENTS 3,596,461 8/1971 Reich 58/28 A 3,456,137 7/1969 Ganter et al. 58/23 TF Primary Examiner-Richard B. Wilkinson Assistant Examiner-Edith C. Simmons Jackmon Attorney- Alex Friedman, Lawrence Rosenthal et al.

[57] ABSTRACT An electric timepiece having a driving circuit having a single coil inserted between the collector electrodes of two transistors, one being of the NPN type, the other being the PNP type. A condenser is inserted between the collector electrode of one transistor and a base electrode of the other transistor, and a bias circuit for supplying self-bias is connected to the base electrode of the two transistors. The driving circuit may be utilized with a time standard oscillator including a tuning fork oscillator. Said tuning fork may be U-shaped, said single coil being mounted intermediate a U-shaped magnetic circuit mounted on a portion of said tuning fork.

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P58 i 59 FIG 1/ I6 VJ- INVENTOR. YUKI TSURUISHI A TTORN E ELECTRIC TIMEPIECE BACKGROUND OF THE INVENTION This invention relates to driving circuits for electric timepieces of both the balance wheel and tuning fork types. In the art, electric timepieces of these types have been provided with driving circuits incorporating both detecting and driving coils. In said circuits, the detecting coil would be connected as an input to the base of the driving transistor, while the driving coil would be connected to the output or emitter-collector path of said driving transistors. One or more pairs of permanent magnets would be fixed to a balance wheel or tuning fork in order to close a magnetic path and the detecting and driving coils are inserted in this magnetic path. The permanent magnets carried by the oscillating balance wheel or tuning fork are positioned so that the magnetic field thereof crosses the two fixed coils to induce a voltage therein responsive to the change of magnetic flux in said coil. The driving transistor of the prior art arrangements is switched by the induced voltage in the detecting coil and electric current flows in the driving coil to maintain the oscillation of the balance wheel or tuning fork.

The energy supplied to the oscillator is a product of the induced voltage v in the driving coil and the current i flowing in said driving coil. If the direct current resistance of the driving coil is R, a Joule loss of Ri is caused by the current i. As this loss does not contribute to the oscillation of the time standard, it must be as small as possible, so that the current i must be as small as possible.

However, if the current i is small, the energy vi supplied to the balance wheel also becomes small, so that the induced voltage v in the driving coil must be increased. Thus, it is most desirable that the voltage v be large, and the current i and resistance R be small. Since the coil must be mounted in a limited space, the induced voltage v can only be increased by using a thin wired coil having a large number of turns. By having only a single coil, rather than both detecting and driving coils, the number of turns of the driving coil can be substantially increased for the same coil space. While driving circuits incorporating a single coil are known in the art, by improving such prior art circuits, substantial advantages are obtained.

Further, by improving the structure of the tuning fork, a more compact and efficient watch structure is produced.

SUMMARY OF THE INVENTION Generally speaking, in accordance with the invention, a driving circuit for an electric timepiece is provided, including time standard oscillator means; and electric circuit means for maintaining the oscillation of said time standard oscillator means, said electric circuit means including a single coil positioned to cooperate with said time standard oscillator means for maintaining the oscillation thereof in response to driving current passed through said coil and a pair of transistors, one of said transistors being of the PNP type and other being of the NPN type. The single coil is inserted between the collector electrodes of the two transistors, while a condenser is inserted between the collector electrode of one of said transistors and a base electrode of the other of said transistor. Bias circuit means is provided for supplying self-bias to the base electrodes of the two transistors; a direct current voltage source is provided to supply energy to said electric circuit means.

The time standard oscillator means may be either a balance wheel or a tuning fork. Where a tuning fork is utilized, said tuning fork is preferably substantially U- shaped and provided with a U-shaped magnetic circuit mounted thereon and encompassing said coil. The U- shaped magnetic circuit may consist of two pairs of spaced mounting plates secured to the ends of the tines of said tuning fork, the two pairs of plates being positioned in adjacent relation with said single coil fixedly mounted intermediate the plates defining each pair. A pair of substantially semi-circular permanent magnets are mounted on the inner surfaces of each of said pairs of plates, to define a separate magnetic circuit passing through said coil, each consisting of one of said pairs of permanent magnets, the associated pairs of mounting plates, and the associated tine of said tuning fork. Said coil is preferably substantially circular.

Accordingly, it is an object of this invention to provide an electric timepiece incorporating a driving circuit having a single coil for both detecting and driving.

Another object of the invention is to provide an electric timepiece having a driving circuit which may be utilized to maintain the oscillation of both balance wheel and tuning fork.

A further object of the invention is to provide an electric timepiece having a tuning fork particularly adapted for assembly in a compact case through the use of mass production.

Still other objects and advantages of the invention will in part be obvious ans will in part be apparent from the specification and drawings.

The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS For a fuller understanding of the invention, reference is had to the following description taken in connection with the accompanying drawings, in which:

FIG. 1 is a cross-sectional view of a balance wheel of one type of electric timepiece wherein permanent magnets are attached to said balance wheel;

FIG. 2 is a plan view of the balance wheel of FIG. 1;

FIG. 3 is a ciruit diagram of one conventional blocking type driving circuit for electric timepieces wherein one coil serves for detecting and driving;

FIGS. 40, b and'c are circuit diagrams of driving circuits for electric timepieces according to the invention;

FIGS. 5a, b and c are wave form diagrams showing output wave forms of the driving circuits of FIGS. 3 and FIG. 6 is a plan view of an electric wrist watch having a tuning fork according to the present invention;

FIG. 7 is a plan view of an end portion of the tuning fork of FIG. 6;

FIG. 8 is a cross-sectional view taken along line A I A of FIG. 2;

FIG. 9 is an enlarged plan view. of the frame of the coil of the watch of FIG. 6;

FIG. 10 is a circuit diagram of another conventional driving circuit for electric timepieces having tuning forks; and

FIG. 11 is a circuit diagram of another embodiment of the driving circuit according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. I, wherein a conventional balance wheel is depicted, l is a balance wheel having upper and lower portions, 2 a balance staff, 3 and 4 are permanent magnets, 5 a single coil, 6 a supporting plate for the coil, and 7 are balancing weights. Four permanent magnets 30 and 3b are secured to the balance wheel of FIG. 2, two of them to the upper balance wheel and the other two to the lower balance wheel. As each balance wheel is made of magnetic material, the magnetic field of each magnet is closed to form two opposite magnetic fields in the space between the upper and lower balance wheels. The coil 5 is disposed at the position where it is linked to said two magnetic fields as shown in FIG. 2.

FIG. 3 is a circuit diagram of a known blocking type of driving circuit wherein 8 is a battery, 9 a coil, I is a PNP type of transistor, 11 a NPN type of transistor, I2 a base resistor, 13 a base bias resistor for PNP type transistor l0, 14 a coupling condenser and 15 a variable resistor for selecting pulse width. This circuit is a self-running blocking type, and the self-running period is determined by the time constant of the resistor 13 and the condenser 14. The pulse width is determined by time constant of condenser 14, the resistor 13 and the internal resistance of the coil 9. Therefore, if the balance wheel is driven by using the above circuit, the self-running period of this circuit should be somewhat longer than oscillating period of the balance wheel, moreover, in order to improve the self-starting characteristics of the balance wheel, the self-running period of the circuit should be stable in the face of changes in the environment. The driving pulse width is determined by circuit constants in spite of increases and decreases in the amplitude of the balance wheel, so that in order to obtain the desirable amplitude, the value of the circuit constant should be precisely selected.

FIG. a shows the driving waveform taken at the collector of transistor II when the balance wheel of FIG. I is driven by the circuit of FIG. 3. As shown in FIG. 5a, the width of a pulse 23 is always constant irrespective of the induced voltage in the coil. Immediately after a pulse is produced by the operation of the blocking oscillator of FIG. 3, the base electrode of PNP type transistor is biased sufficiently in the forward direction, so that a double driving pulse can not be produced. Therefore, when the balance wheel is driven in both directions during each reciprocation, an undersired pulse is produced as shown in FIG. 5a so that the isochronism of the balance wheel is disturbed.

As mentioned above, the value of the circuit components of the circuit of FIG. 3 should be selected precisely, but the value of condenser 14 generally must be more than several thousand PF and it is worth the high initial cost to select the tolerance of the said condenser value within a short range. As more particularly described below, the arrangement according to the invention provides a stabilized driving circuit wherein the defects of the conventional types of driving circuits are eliminated and a wide tolerance range of values of components is permitted. Further, the driving method is such that the balance wheel can self-start in both directions and can be driven alternately.

FIG. 41 shows three embodiments of the driving circuit according to the invention wherein I6 is an electric source of direct current, 17 a PNP type transistor, 18 a NPN type transistor, 19 a coil, 20 a base resistor for PNP type transistor 17, 21 a condenser, and 22 a base bias resistor for NPN type transistor 18. This circuit is characterized by the fact that FNP type transistor 17 and NPN type of transistor I8 are generally maintained. in an operating region of linear characteristics, and that even a small quantity of detecting voltage induced in the coil can be directly amplified. The self-starting characteristics of the balance wheel in the embodiments of FIGS. 3a and b are higher and more stabilized than in the embodiment of FIG. 3c. The two driving transistors incorporate self-biasing means wherein the base and the collector electrodes of the transistors are coupled by resistors. Therefore, the driving circuit according to the invention produces highly reliable selfstarting, and as the base potential of the transistors are not fully biased by a small charge in the condenser, double pulses are symmetrically produced, so that the balance wheel is driven alternately without disturbing the isochronism, as shown'in FIG. 5b.

FIG. 5b and FIG. 50 show the wave forms when the balance wheel of FIG. I is driven by using a circuit of FIG. 4 according to the invention. FIG. 5b shows the voltage wave form at the collector electrode of transistor I8, and FIG. 50 shows a voltage wave form at the collector electrode of the transistor 17. As understood from FIG. 5b, when the induced voltage of the coil is large, a wide pulse 24 is produced and when the induced voltage is small, a narrow pulse 25 is produced. Therefore, the pulse width is not determined only by the circuit constants, so a wide tolerance in the range of values of components can be permitted.

The driving circuit according to the invention is particularly useful as the driving circuit of an electric timepiece having a balance wheel, because the balance wheel can self-start and be driven alternately by the stabilized driving circuit, and efficiency is increased since the coil serves for both detecting and driving.

However, the circuit according to the invention can be used as the driving circuit not only for a balance wheel but also for an oscillator such as a tuning fork.

Referring now to FIG. 6, wherein the mechanism of a wrist watch according to the invention is depicted, 31 is a voltage source of direct current, 32 a tuning fork, 33 a coil, 34 a magnet plate, 35 a frame for supporting coil 33, 36 a ratchet wheel, 37 a block containing the driving circuit, 38 a connecting terminal connecting a negative pole of the battery 31 to circuit block 32, and 39 a connecting terminal connecting the coil 33 to the circuit block 37. The diameter of battery 31 is generally somewhat smaller than a radius of a movement of the wrist watch, and the tuning fork 32 is provided with curved tines in order to incorporate the battery 31. The end portion of the tuning fork 32 is connected to mounting plates 34 of magnetic material by pins 40 as shown in FIG. 7. An upper plate. 34a and lower plate 34b is mounted on the end of each tine of tuning fork 32 as shown in FIG. 8. Permanent magnets 41a and 41b are respectively fixed in facing relation on the inner surfaces of each pair of mounting plates 4a and 412. The polarities of the permanent magnets 41a and 41b are disposed to produce a closed magnetic circuit wherein the magnetic flux passes through the space between the magnets, through both mounting plates 34a and 34b,

and through the tine of tuning fork 32. However, only one magnet may be provided on either the upper or lower plate. The coil 33 is inserted in thespace between magnets 41a and 41b. The end portions of both tines of the tuning fork 32 are formed symmetrically, so that the completed tuning fork 32 is provided with tines which are symmetrically shaped. Permanent magnets 41a and 41b are semi-circular in shape to cooperate with the round coil 33. I

The coil 33 is fixed to the frame 35 as shown in FIG. 9, and inserted in the space between the permanent magnets at the end portion of the tuning fork leaving a proper space in order that said coil does not contact tuning fork 32. Frame 35 is fixed to the plate of the watch. Electrically conductive portions 42 and 43 are formed on frame 35 in order to receive a lead wire of the coil 33. Frame 5 includes a printed board having a thin copper plate disposed therein, a pattern defining conductors 42 and 43 being etched in said plate by an etching reagent.

In the embodiments of the present invention, the conductive portion 42 of coil frame 45 serves to receive one end of the lead wire of coil 33 and to connect circuit block 37 with the negative pole of the battery. The conductive portion 43 serves to receive the other end of the lead wire of the coil 33. I

The tuning fork according to this invention may be energized by a coil 3 having its two terminals connected to the driving circuit shown in FIG. 10, wherein 44 is a battery, 45 a coil, 46 a NPN type transistor, 47 a PNP type transistor, 48 a base resistor of said NPN type transistor 46, 49 a trigger condenser, 50 a variable resistor for regulating the amplitude of the tuning fork, and 51 a base resistor for the PNP type transistor 17. This circuit is known as an astable blocking oscillator.

FIG. 11 shows one embodiment of the circuit according to the invention which is particularly suitable for driving the tuning fork according to this invention. 52 is a battery, 53 a PNP type transistor, 54 a NPN type transistor, 55 a coil, 56 a trigger'condenser, 57 a base bias resistor for NPN type transistor 54, 58 a base resistor for PNP type transistor 53, 59 a decoupling condenser for preventing the oscillation of the harmonic wave, and 60 a variable resistor regulating amplitude. By use of such a circuit, the tuning fork can be surely driven by a single coil, and a very advantageous construction can be achieved. The variable resistor for adjusting the amplitude can be removed if desired.

The wrist watch having tuning fork in accordance with the present invention offers substantial advantages as compared with the conventional type of wrist watches having a tuning fork. Thus, as the coil and the frame of the coil are inserted in the space between the magnets from the end of the tuning fork, the coil can be mounted and removed without displacing the tuning fork so that quick assembly can be assured and auto matic assembly can be easily carried out.

Further, the magnetic field produced by the magnets covers almost the whole coil, the strength of the magnetic field on a surface of the coil is almost uniform, and its strength can be increased. For this reason, sufficient flux density can be obtained from a relatively thin magnet, the turns of the coil can be reduced to about A: of the number of the conventional coil, and a thin wrist watch having a tuning fork can be obtained.

Still further, a single coil having two terminals is used for both detecting and driving, so the winding of the coil for mass be performed quickly, an arrangement which is very advantageous fomass production. Moreover, heretofore two coils are used, one each in the right and left portions, while, in the invention, only one coil may be sufficient.

Finally, one portion of the tuning fork according to the invention is used as part of the magnetic path, so that it is not necessary to weld the tuning fork and the end portion by a silver solder. Rather, the end portion can be easily secured by a pin or a screw. The tuning fork is formed of a material with constant elasticity in response to the temperature changes in order to constantly maintain the frequency of the tuning fork. It is not desirable to heat-treat such material at high temperature, as by silver soldering. Accordingly, the construction of the invention is advantageous for maintaining the characteristics of the tuning fork.

It will thus be seen that the objects set forth above, and those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in the above constructions without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

What is claimed is:

1. In an electric wrist watch having a tuning fork as an oscillator, the improvement which comprises said tuning fork being substantially U-shaped and having a pair of oscillating tines, said watch including a U- shaped magnetic circuit mounted at the end of each of said tines and a single coil positioned in the path of both of said magnetic circuits for cooperation therewith to sustain the oscillation of said tuning fork, each of said magnetic circuits including a pair of spaced mounting plates secured to the end of said tine, and a pair of permanent magnets mounted in spaced facing relation on the inner surface of said plate, said coil being positioned intermediate said permanent magnets, the magnetic flux flowing through each magnetic circuit passing between the permanent magnets of each of said magnetic circuits through said coil, along said mounting plates and through a portion of the tine associated therewith.

2. A wrist watch as recited in claim 1, wherein said coil is substantially circular in shape, each of said per- 7 manent magnets being substantially semi-circular and overlapping said substantially circular coil.

3. A wrist watch as recited in claim 1, including a substantially circular battery mounted in said wrist watch, said tuning fork tine each including a substantially symmetrical curve portion for permitting the accommodation of said battery adjacent one of said tines.

4. A wrist watch as recited in claim 1, including driving circuit means having a NPN transistor and a PNP transistor, each of said transistors having a base, emitter and collector, said single coil being connected between the collector terminals of said two transistors.

5. A wrist watch as recited in claim 4, wherein said driving circuit means includes a condenser inserted between the collector electrode of one of said transistors and a base electrode of the other of said transistors, and

bias circuit means for supplying self-bias to the base electrodes of said two transistors.

6. A circuit as recited in claim 5, wherein said condenser is inserted between the collector of said PNP transistor and the base of said NPN transistor, said bias circuit means including resistors connected between the base of each of said transistors and the collector of said NPN transistor.

7. An electric circuit as recited in claim 5, wherein said condenser is inserted between the collector electrode of said NPN transistor and the base of said PNP transistor, said bais circuit means including resistors connected between the respective bases of said two transistors and the collector of said PNP transistors.

8. An electric circuit as recited in claim 5, wherein said condenser is inserted between the collector of said PNP transistor and the base of said NPN transistor, and

said bias means includes a first resistor connected between the base of said PNP transistor and the collector of said NPN transistor, a second resistor connected between the base of said'NPN transistor and the emitter of said PNP transistor.

9. A circuit as recited in claim 5, wherein said condenser is inserted between the collector of said PNP transistor and the base of said N PN transistor, said base bias means including a first resistor connected between the base of said PNP transistor and the collector of said NPN transistor, and second resistor connected between the base of the NPN transistor and the collector of said PNP transistor.

10. A circuit as recited in claim 9, including a decoupling condenser connected between the base and collector of said NPN transistor.

11. A circuit as recited in claim 9, including a variable resistor connected in series with said coil for adjusting the amplitude of the pulses therethrough. 

1. In an electric wrist watch having a tuning fork as an oscillator, the improvement which comprises said tuning fork being substantially U-shaped and having a pair of oscillating tines, said watch including a U-shaped magnetic circuit mounted at the end of each of said tines and a single coil positioned in the path of both of said magnetic circuits for cooperation therewith to sustain the oscillation of said tuning fork, each of said magnetic circuits including a pair of spaced mounting plates secured to the end of said tine, and a pair of permanent magnets mounted in spaced facing relation on the inner surface of said plate, said coil being positioned intermediate said permanent magnets, the magnetic flux flowing through each magnetic circuit passing between the permanent magnets of each of said magnetic circuits through said coil, along said mounting plates and through a portion of the tine associated therewith.
 2. A wrist watch as recited in claim 1, wherein said coil is substantially circular in shape, each of said permanent magnets being substantially semi-circular and overlapping said substantially circular coil.
 3. A wrist watch as recited in claim 1, including a substantially circular battery mounted in said wrist watch, said tuning fork tine each including a substantially symmetrical curve portion for permitting the accommodation of said battery adjacent one of said tines.
 4. A wrist watch as recited in claim 1, including driving circuit means having a NPN transistor and a PNP transistor, each of said transistors having a base, emitter and collector, said single coil being connected between the collector terminals of said two transistors.
 5. A wrist watch as recited in claim 4, wherein said driving circuit means includes a condenser inserted between the collector electrode of one of said transistors and a base electrode of the other of said transistors, and bias circuit means for supplying self-bias to the base electrodes of said two transistors.
 6. A circuit as recited in claim 5, wherein said condenser is inserted between the collector of said PNP transistor and the base of said NPN transistor, said bias circuit means including resistors connected between the base of each of said transistors and the collector of said NPN transistor.
 7. An electric circuit as recited in claim 5, wherein said condenser is inserted between the collector electrode of said NPN transistor and the base of said PNP transistor, said bais circuit means including resistors connected between the respective bases of said two transistors and the collector of said PNP transistors.
 8. An electric circuit as recited in claim 5, wherein said condenser is inserted between the collector of said PNP transistor and the base of said NPN transistor, and said bias means includes a first resistor connected between the base of said PNP transistor and the collector of said NPN transistor, a second resistor connected between the base of said NPN transistor and the emitter of said PNP transistor.
 9. A circuit as recited in claim 5, wherein said condenser is inserted between the collector of said PNP transistor and the base of said NPN transistor, said base bias means including a first resistor connected between the base of said PNP transistor and the collector of said NPN transistor, and second resistor connected between the base of the NPN transistor and the collector of said PNP transistor.
 10. A circuit as recited in claim 9, including a decoupling condenser connected between the base and collector of said NPN transistor.
 11. A circuit as recited in claim 9, including a variable resistor connected in series with said coil for adjusting the amplitude of the pulses therethrough. 